Blind man navigates obstacle course perfectly
In a recent experiment, a completely blind patient navigated a complicated obstacle course flawlessly, providing researchers with an opportunity to assess just what kind of 'sight' is possible without a functioning visual cortex. The study, published in the journal Current Biology, was funded in part by the EU's Sixth Framework Programme (FP6) under the New and Emerging Science Technologies Theme. The patient, called TN, had suffered two strokes in succession that caused extensive damage to both sides of his brain, including the visual cortex (the region of the brain that is responsible for processing visual information). A team of researchers from the Netherlands, the UK, Italy, Switzerland and the US studied TN behaviourally and physically, using functional and anatomical brain imaging such as diffusion tensor imaging (DTI), retinotopic mapping, computer-based perimetry and psychophysical testing. These extensive tests confirmed that TN completely lacked any functional visual cortex. It was important for the researchers to thoroughly establish TN's total blindness because he had previously exhibited 'blindsight', in which he responded to the facial expressions of others and to visual 'fear conditioning' tests. All tests did in fact show that TN's visual cortex could not function; he also walks using a stick to detect obstacles, and requires guidance by another person when walking around buildings. Next, the researchers constructed a complex obstacle course down a long hallway using boxes and chairs. TN was asked to walk down the hallway, without the use of his cane or guidance from another person. The hallway was quiet, and neither TN nor the person following him for safety made any noise beyond the sounds of their steps. Incredibly, TN navigated the course perfectly, never once colliding with an obstacle. When he reached the end of the maze, several witnesses applauded spontaneously. TN's case provides inspiration for researchers looking for alternative visual paths in the brain, and shows how people may orient themselves and navigate around obstacles without any conscious attention or experience of seeing them. According to Dr Beatrice de Gelder of Tilburg University in the Netherlands, 'It's a part of our vision that's for orienting and doing in the world, rather than for understanding. All the time, we are using hidden resources of our brain and doing things we think we are unable to do.' The possibility that TN navigated the course using echolocation (the reverberation of sound waves off nearby objects) cannot be ruled out; however, the silence of the experiment makes this an extremely unlikely explanation. It is not clear which of the many possible brain pathways are responsible for TN's intact navigation skills. The lack of similar cases makes speculation in this area difficult. The only prior study was of a monkey (named Helen) with similar astonishing abilities. Helen's researchers concluded that she had a small region of intact peripheral vision, although this could not account for all of her residual vision functions. 'This is absolutely the first study of this ability in humans,' said Dr de Gelder. 'We see what humans can do, even with no awareness of seeing or any intentional avoidance of obstacles. It shows us the importance of these evolutionarily ancient visual paths. They contribute more than we think they do for us to function in the real world.'
Countries
Switzerland, Italy, Netherlands, United Kingdom, United States